Process for depositing a film

ABSTRACT

A coating composition comprising (1) from about 40% to about 95%, by weight, of an anionic acrylic polymer containing at least a carboxyl or alcoholic hydroxyl function, (2) from about 4.9% to about 50%, by weight, of an amine-aldehyde cross-linking agent and (3) from about 0.1% to 10%, by weight, of an acyclic trisulfone is provided. The composition finds utility in coating applications wherein low temperature cure of the said coated resinous compositions can be obtained with attendant high resistance to organic solvents.

United States Patent Parekh et al.

[ Nov. 26, 1974 PROCESS FOR DEPOSITING A FILM [75] Inventors: Girish Girdhar Parekh, Stamford;

Werner Josef Blank, Wilton, both of Conn.

[73] Assignee: American Cyanamid Company,

Stamford, Conn.

['22] Filed: Oct. 2, 1972 [21] App]. NO.: 294,041

Related U.S. Application Data [62] Division of Ser. No. 130,526, April 1, 1971, Pat. No.

[52] US. Cl. 204/181, 117/132 B [51] 1nt.Cl B0lk 5/02, 844d 1/36, C23b 13/00 [58] Field of Search 204/181; 117/132 B 3,681,224 8/1972 Stromberg 204/181 Primary Examiner-Howard S. Williams Attorney, Agent, or FirmEvans Kahn 57 ABSTRACT A coating composition comprising (1) from about 40% to about 95%, by weight, of an anionic acrylic polymer containing at least a carboxyl 0r alcoholic hydroxyl function, (2) from about 4.9% to about 50%, by weight, of an amine-aldehyde cross-linking agent and (3) from about 0.1% to 10%, by weight, of an acyclic trisulfone is provided. The composition finds utility in coating applications wherein low temperature cureof the said coated resinous compositions can be obtained with attendant high resistance to organic solvents.

9 Claims, No Drawing s PROCESS FOR DEPOSITING A FILM This application is a divisional of our copending application, Ser. No. 130,526, filed on Apr. 1, 1971, now US. Pat. No. 3,723,374.

BACKGROUND AND DESCRIPTION OF PRIOR ART Water dispersed polymeric coating compositions havebeen employed to coat metallic surface as by hand or automatic spray painting, electrostatic painting, brushing, dipping and, more recently, by electrodeposition. The latter method has been gaining in acceptance because electrodeposition can be used to coat shaped metallic surface uniformly. However, none of the methods is wholly satisfactory. Although good uniformity, film strength, hardness and adhesion are noted in US. Pat. No. 3,403,088 to Donald P. Hart, issued on Sept. 24, 1968 and US. Pat. No. 3,471,388 to J. N. Koral, issued on Oct. 7, 1969, a difficult problem is presented where low temperature curing of electrocoated metallic objects is required, due to the heat sensitivity of the metallic object. As is known, distortion of the crystalline structure of aluminum, a metal widely used in the aircraft industry, takes place at temperatures in excess of about 275F. Such temperatures, and even higher, are normally required to effect curing of the electrodeposited polymeric coating composition so as to cause that composition to harden. Nonetheless, such elevated temperatures cannot be universally employed, because the coated surface of certain metals, or metals to which rubber or plastic fittings are attached,

requires the use of temperatures sufficiently high to effect the cure, while simultaneously adversely affecting the. metal substrate or attachments thereto. For instance, in the patent to Hart, above-identified, curing of a partially neutralized acrylic interpolymer containing at least carboxyl and hydroxyl groups and an aminealdehyde condensation product, when applied to a me tallic surface, as for instance, aluminum, occurs at elevated temperatures of at least 350F. Where such temperatures are used and, even higher, as for instance, 500F., distortion of the microcrystalline structure of an aluminum substrate occurs. Further, cured coated articles are frequently affected by organic solvents, as, for example, acetone or methyl ethyl ketone. Still further, many baths containing coating compositions are not wholly satisfactory, because they are found to be relatively unstable and require replacing or replenishing at frequent intervals which is both time and treasure consuming.

SUMMARY A three component composition of matter which can be used effectively in the coating of metallic articles by conventional techniques and particularly by electrophoretic techniques followed by heat curing at low temperatures hitherto unavailable, has been discovered. Non-distorted, unifonnly coated metallic articles with attendant resistance to detergents, salt spray and most organic solvents have been prepared.

DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS As one component of a three component system, there is provided an acrylic, anionic water dispersible, non-gelled polymer containing carboxyl and alcoholic hydroxyl functions. In addition, the anionic polymer carboxyl groups and alcoholic hydroxyl groups as well chlorostyrenes,

as amide groups.

All of these anionic, water dispersible, non-gelled polymeric materials having carboxyl groups and/or alcoholic hydroxyl groups and/or amide groups have water sensitive sites obviously, by virtue of the presence of these groups, and these water sensitive sites should be tied up by interreaction with the second component of the system, namely, an amino-aldehyde compound in a cross-linking mechanism. Before the crosslinking takes place, the amino-aldehyde compounds also function as plasticizers for the total composition.

The anionic polymeric materials prepared by vinylpolymerization may be prepared in either an aqueous solution, an organic solvent, or in an aqueous emulsion system, all of which procedures are thoroughly well known in the art, and it is not believed to be neces sary to elaborate on such procedures here.

The acrylic polymers may be prepared by polymerizing polymerizable monomers such as acrylic acid, methacrylic acid, crotonic acid, ciinnamic acid, B-benzoyl acrylic acid, amd polycarboxylic acids of the ically, chloromaleic acid, and the like. These acidic ma-- terials' may be copolymerized or polymerized with other monomers which contain no carboxyl groups, such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, decyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, heptyl methacrylate, decyl methacrylate, propyl crotonate, butyl crotonate, nonyl crotonate, and the like. Still further, one could use such polymerizable compounds as styrene, ortho-, or para-alkyl styrenes such as the 0-, m, or p-methyl, ethyl, propyl and butyl styrenes, 2,4-dimethyl styrene, 2,3-dimethyl styrene, 2,5-dimethyl styrene, vinyl naphthenate, acrylonitrile, methacrylonitrile, halo-ring or side-chain styrenes, such as a-chloro styrene, orthometa-, or para- 2,4-dichlorostyrene, 2,3- dichlorostyrene, 2,5-dichlorostyrene or the alkyl sidechain styrenes, such as a-methyl styrene, a-ethyl styrene, and the like. Additionally, one can make use of such polymerizable vinyl monomers as acrylarnide, methacrylamide, ethacrylamide, N-tertiarybutylacrylamide, and the like.

The anionic polymeric materials containing alcoholic hydroxyl groups are prepared by using a polymerizable vinyl monomer which contains an alcoholic hydroxyl and is to be found in such compounds as the hydroxyalkyl esters of B-unsaturated monocarboxylic acids such as the hydroxyalkylesters of acrylic acid, methacrylic, ethacrylic and chloro as well as the other chloro substituted acrylic acids. These esters may either have a primary or a secondary hydroxyl group. 11- lustrative of the types of compounds that are used to make the copolymers in the anionic, polymeric material are Z-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 3-hydroxybutyl acrylate, 4-hydroxybutyl acrylate, 8-hydroxyoctyl acrylate, 2-hydroxyethyl methacrylate, 5-hydroxyhexylmethacrylate, 6-hydroxyoctylrnethacrylate, 8-hydroxyoctylmethacrylate, 10-hydroxydecylmethacrylate, 3-hydroxypropyl crotonate, 4' hydroxyamyl crotonate, 5-hydroxyamyl crotonate, 6- hydroxyhexyl crotonate, 7-hydroxyheptyl crotonate, IO-hydroxydecyl crotonate, and the like. These hydroxy esters are used in combination with one another with other polymerizable vinyl monomers devoid of any alcoholic hydroxyl group including those set forth hereinabove in the discussion of the carboxyl groupcontaining monomers. Additionally, one can make use of similar acetal-containing polymerizable vinyl monomers, such as methoxymethylacrylamide, methoxymethylmethacrylamide, and the like.

Among the amide group-containing monomers which may be used in the preparation of the anionic, water dispersible, polymeric material used in the present invention are: acrylamide, methacrylamide, ethacrylamide, and the like. These polymerizable acrylamides may be used to prepare anionic polymeric materials used in the present invention with any of the carboxyl group-containing monomers or the hydroxyl groupcontaining monomers or with any of the polymerizable monomers set forth hereinabove.

To obtain a satisfactory balance of properties, that is, good electrocoating bath stability, low cure tempera ture (i.e., from 210F. to 260F.), good corrosion and humidity resistance of the coating as well as smoothness and blister-free appearance, it is advantageous to utilize. anionic polymers containing from about 1.0% to about 25%, and preferably from 4% to of monomer units providing carboxyl groups and from 0.5% to 10%, and preferably from 1.5% to 4%, of monomer units providing hydroxyl groups, all percentages based on the weight of the overall finished polymer.

In general, the finished polymer will exhibit the following properties: Acid No. 55 to 95; Hydroxyl No. 44 to 95; Viscosity: Z to 2 (when solids equal 50% to 80%); and a Gardner color from 1 to 12.

The second component of the mixture containing the hereinabove defined polymer is 'an amino-aldehyde cross-linking agent. For coating applications other than electrocoating, there may be used any amino crosslinking agent whether fully etherified, partially etherified or unetherified. However, for electrocoating applications, the use of fully etherified amino-aldehyde cross-linkers is required. Usually, the latter aminoaldehyde cross-linking agents are present in amounts ranging from about 4.9% to about 50%, and the balance being principally the polymer containing at least carboxyl and/or hydroxyl groups. Advantageously, any fully etherified amino cross-linking agent can be incorporated herein, as for instance, hexakismethoxymethylmelamine which is prepared according to the process shown in U.S. Pat. No. 2,998,411, which patent is incorporated herein by reference. Modification of the hexakismethoxymethylme[amine is shown in U.S. Pat. No.'3,47l,388 wherein a mixture of substantially water-insoluble, substantially fully etherified hexamethylolmelamines which have no more than four methoxy methyl groups on the average and at least two alkoxy methyl groups selected from the group consisting of ethoxy methyl, propoxy methyl and butoxy methyl. These mixed fully etherified hexamethylolmelamine compounds are disclosed in said patent and incorporated herein by reference. Additionally, the fully etherified tetramethylolbenzoguanamine compounds may also be used, such as those disclosed in U.S. Pat. No. 3,091,612 and in earlier U.S. Pat. Nos. 2,197,357 and 2,454,495, all of which are incorporated herein by reference.

The third component of the mixture containing any of the hereinabove defined polymers and cross-linking agents are the acyclic trisulfones or tris(alkyl sulfonyl)methanes represented by the structure:

where R R and R each alkyl radicals of from 1 to 18 carbon atoms, or aromatic radicals, such as phenyl or naphthyl, which may be the same or different. Alkyl groups of from 6 to 12 carbon atoms are preferred.

The trisulfones are usually present in amounts ranging from about 0.1% to about 10%, based on the overall polymer and crosslinking agent mixture. The methods for preparing such trisulfones are well known as disclosed in U.S. Pat. No. 3,337,636 which is incorporated herein by reference. Illustrative trisulfones which are particularly effective in permitting low temperature curing of anionic acrylic polymers in admixture with amino-aldehyde cross-linking compounds are:

tris(methylsulfonyl)methane,

tris( ethylsulfonyl )methane,

tris-( n-propylsulfonyl )methane,

tris-(isopropylsulfonyl)methane,

tris-( t-butylsulfonyl )methane,

tris-(n-pentylsulfonyl)methane,

tris-(n-hexylsulfonyl)methane, tris-(n-heptylsulfonyl)methane,

His-(dodecylsulfonyl)methane,

bis-( methylsulfonylHoctadecylsulfonyl)methane,

bis-( phenylsulfonyl dodecylsulfonyl )methane,

bis-( naphthylsulfonyl dodecylsulfonyl )methane,

tris-(phenylsulfonyl)methane, and

tris-(naphthylsulfonyl)methane.

The trisulfonylmethanes are also found to be particularly useful, since they are compatible with and stable in the polymer environment of the present invention.

The anionic polymer, the fully etherified amino cross-linking agent and the acyclic trisulfone are admixed with agitation. Usually, a neutralizing agent such as either an inorganic base, such as sodium hydroxide or an organic amine, such as a lower alkylamine, or a lower alkanolamine as for instance, diethylamine, triethylamine, or diisopropanolamine is added to effect solubilization of the polymer, in amounts ranging from 1% to 10% by weight of the polymer.

It has been found that a satisfactory electrocoating bath can be prepared from the aforementioned mixture by blending the same with deionized water to efiect its emulsification. It is good practice to next age the emulsifted blend for a period of 24 hours. The solids content of the bath is maintained at from 1% to 20%, and preferably from 5% to based on the overall weight of the emulsion. The preferred concentration of the tris-(alkylsulfonyl)methane in the bath is between 0. 1% and 0.5%.

, Although formulations of the above components find utility in the areas of conventional organic coating, adhesives and thermoset resins, it finds particular utility in electrodeposition techniques, since the properties of electrocoated surfaces are markedly enhanced, as for instance, resistance to corrosion, solvent exposure and bath stability.

Electrodeposition is effected at room temperature in the conventional manner by utilizing a metallic substrate as an anode and any metallic surface as the cathode by applying a potential of from volts to 500 volts, and preferably from 50 volts to 200 volts, across the electrodes. Generally, sixty seconds are sufficient to accomplish the electrocoating process.

The coated substrate is next water washed, usually with deionized water, and heat cured to effect crosslinking of the polymer of the present invention. Significantly, this can be accomplished at temperatures rang ing from about 210F. to not more than about 260F., whereby distortion of the crystalline structure of the coated metal so heated does not occur. However,

where distortion of the crystalline structure of the may be employed, if desired. Further, the coated cured surface is impervious to organic solvents.

It is also within the scope of the present invention to incorporate various dyes, and pigment additives to impart color to the novel polymeric compositions. For instance, compatible dyes or pigments such as TiO Fe 0 metal chromates, such'as lead or strontium chr0- mate, or carbon black can be used, such that the resultant electrocoated metal substrate is white, red, yellow, black or any desired color. Usually, the amounts of pigment incorporated therein range from about 0.1% to about 6% of the overall coating bath.

The following examples are set forth primarily for purposes of illustration and any specific enumeration of detail contained therein should not be interpreted as a limitation except as is indicated in the appended claims. All parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 A polymer derived from 39% butyl acrylate, 11% 2- hydroxyethyl acrylate, 11% acrylic acid and 39% styrene is prepared in ethyl amyl ketone, utilizing azobisisobutyronitrile as the catalyst at 85C. by well known techniques. The polymer analyzes as having an acid number of 85, an hydroxyl number of 55 and a viscosity of 150 poises.

77.0 Parts of a 70% hereinabove prepared polymer solution (in ethyl amyl ketone-ethylene glycol monoethyl ether) are blended to form a paste with a mixture of 22.0 parts of tetra(ethoxymethyl)di(methoxymethyl)melamine cross-linking agent, 3 parts of diethylamine and 23.0 parts of titanium dioxide pigment. Resultant paste is next emulsified in 860 parts of deionized water. To this emulsion are added 2.0 parts of tris-(hexylsulfonyl)methane (dissolved in 1 part of diethylamine and 25 parts of a 1:1 2-ethoxyethanol/water mixture). The emulsion, aged for 24 hours, is placed in an electrocoating bath.

' There is inserted into the latter bath a stainless steel plate which is used as a cathode and a zinc-phosphated cold-roller steel panel which is used as the anode. A potential of 100 volts to 300 volts is applied for from one to three minutes. The anode is next removed, washed with deionized water and the excess water blown off. The coated panel is next baked at about 250F. 260F. for 20 minutes.

The coated panel of 0.6 mil thickness, is resistant to organic solvents such as acetone, and methyl ethyl kctone, and possesses a Knoop hardness of 9.25.

Similar results are obtained where tris- (phenylsulfonyl)methane is substituted for tris-(hexylsulfonyl)methane in the electrocoating bath.

EXAMPLE 2 The procedure of Example 1 above is repeated except that the tris-(hexylsulfonyl)methane adjuvant is omitted from the electrocoating bath. A coating is deposited at the same film thickness onto the same uncoated panel, washed and cured at about 250F. 260F. for 20 minutes. The panel is found to be soft, of Knoop hardness equal to 1.5 and exhibited no resistance to organic solvents. Acetone, for instance, dissolved the coating.

EXAMPLE 3 81 Parts of a polymer solution in ethyl amyl ketone-ethylene glycol monoethyl ether as defined in Ex ample 1 above are blended with 23 parts of tetra(methoxymethyl)benzoguanamine-salicylic acid as a crosslinking reagent. To this blend are next added 3.6 parts of diethylamine and 23.0 parts of titanium dioxide to form a paste. Resultant paste is emulsified in 860 parts of deioniZed water. To the latter emulsion are added 2.0 parts of tris(hexylsulfonyl)methane in the form of an aqueous diethylamine solution. 230-.

An electrocoating bath is prepared as in Example 1 above and electrodeposition is accomplished at 300 volts for a minute. The coated panel is rinsed with deionized water and baked at 250F. 260F. for 20 minutes. A film having a 0.8 mil thickness is obtained.

The film is totally resistant to organic solvents and exhibited a Knoop hardness of 14.2.

Repeating the procedure of the above and utilizing tris-(dodecylsulfonyl)methane in lieu of tris-(hexylsulfonyl)-methane, similar results in the coating of the panel are noted.

EXAMPLE 4 Repeating the procedure of Example 3 above in every detail except that the trisulfonyl methane additive is omitted, the electrodeposited cured film is found to be soft and sticky.

EXAMPLE 5 Curing of the deposited film occurred at about 300F. for 20 minutes at which time a film thickness of 0.8 mil is measured. The film is totally resistant to the organic solvents of Examples 1 and 3 above.

EXAMPLE 6 100 Parts of a 50% solution of the polymer prepared in Example 1 above are blended with 20 parts of hexakis(methoxymethyl)melamine.

Draw down films which were prepared from this blend were cured at 300F. for 20 minutes and found to be soft and sticky, indicating no resistance to solvent attack.

EXAMPLE 7 The procedure of Example 6 is repated in every respect except that 0.2 parts of tris-(hexylsulfonyl)methane, dissolved in 5 parts of 2-ethoxyethanol, is added to the polymer-curing agent coating composition.

Draw down films which were prepared from this modified blend were cured at 250F. for 20 minutes and found to be resistant to acetone and methyl ethyl ketone.

EXAMPLE 8 Into a suitable reaction vessel there is introduced for purposes of preparing a polyester 150 parts of tall oil fatty acids and the acid number of the charge is determined. There is then added 365 parts of 4-oxatricyclo (6 2 l 0 )-undecan-9-(10)-ol. The materials are mixed together and the acid number of the blend is determined. The acid number of the blend should be about 80.5 i 0.5% of the acid number as originally determined. The charge is then heated under an inert blanket of nitrogen gas or carbon dioxide to a temperature of 230 235C. using an open stack. The charge is held for 5 hours at that temperature. Subsequent to the 5 hour period, the acid number is determined every hour and when the acid number drops to below about 10, the mass is cooled to about 200C. and the viscosity reading is taken on a sample on the Gardner-Holdt scale at 25C. The inert gas flow is reduced and it is switched to an inert blanket. There is then added 22 parts of maleic anhydride, while the mass is held at around 200C. to 210C. The mass with constant stirring is heated over a period of time from to 30 minutes to a temperature of 230C. 235C. When the charge reached 230C. 235C. it is held at that temperature for about 90 minutes. Thereupon the mass is cooled to about 145C. 150C. and viscosity determinations are taken on samples again under the Gardner- Holdt scale at 25C. A reflux condenser is then attached to the reaction system followed by the addition of 22 parts of diacetone alcohol, an inert organic solvent and the mass is then refluxed at about 145C. 150C. The batch is maintained at 145C. 150C. There is prepared separately a blend of 77 parts of monomeric styrene, 8.8 parts of acrylic acid, 1.75 parts ditertiarybutyl-peroxide and 0.44 part of ndodecylmercaptan. The blend of these components is then fed into the reaction system over a period of about 100-l20 minutes. The reflux is maintained throughout the whole reaction. The temperature drops slightly during the addition of the blend to about 135C. 140C. After the addition is finished, the batch is then held at about 135C. 140C. for about 2 hours. Subsequent EXAMPLE 9 This example illustrates the preparation of an electrocoating bath utilizing the polyester resin prepared in accordance with Example 8 above.

Into a suitable reaction vessel used for mixing purposes, there is introduced parts of the resin composition prepared according to Example 8, above. Additionally, there is added the following components: 16.5 parts of a fully etherified melamine aldehyde crosslinking agent, 2.8 parts of diethylamine, 33 parts of rutile titanium dioxide and 860 parts deionized water in the order set forth hereinafter. The cross-linking agent, namely, the tetraethyl dimethyl ethers of hexamethylol melamine, and the diethylamine are added to the resin initially, followed by the addition of the titanium dioxide. The mixture is next ground into a paste on a threeroll mill. Under high speed agitation, the deionized water is added in small portions to the paste. When phase inversion takes place, the rest of the deionized water can be added in one portion. This bath is agitated for 24 hours prior to use. The 10% solids paint is poured into a steel container acting as a cathode. The metal piece to be coated acting as an anode is inserted into the bath. A potential of 200 volts across the electrodes is employed for one minute. The film deposited on the metal piece is rinsed with deionized water and baked for 20 minutes at 300F. The coating is found to be soft and soluble in acetone.

EXAMPLE l0 Repeating Example 9 in every detail except that 0.4 part of tris-(hexylsulfonyl)methane (dissolved in 10 parts of 2-ethoxyethanol/water (1:1) mixture andv 0.5 part of diethylarnine) is added to the electrocoating bath. A hard and solvent resistant coating is obtained. Acetone, for instance, did not affect the resultant coatmg.

We claim:

I. In a process for hard-coating a metal substrate, the improvement which comprises: coating said metal sub strate with a water dispersed composition comprising (A) from about 40% to about by weight, of an anionic acrylic polymer, said polymer containing from 2.5% to 50% by weight of monomer units providing carboxyl groups or from 0.5% to 10% by weight of monomer units providing alcoholic hydroxyl groups or mixtures of the same, (B) from about 4.9% to about 50%, by weight, of an amino aldehyde cross-linking agent, said agent being unetherified, partially or completely etherified, and (C) from about 0.1% to about 10%, by weight, of a tris sulfonyl methane having the structure:

wherein R R and R are each an alkyl radical of from 1 to 18 carbon atoms or an aromatic radical, while radicals are the same ordifferent,

said percentage of (C) being based on the overall solids content of said (A) and (B), depositing a film ranging from about 0.6 to about 1 mil in thickness, heat treating the so-coated metal substrate at a temperature from about 2l0F. to about 350F., and recovering a hard-coated substrate impervious to organic solvents.

2. The process according to claim 1 wherein the coating is accomplished by a dipping technique.

3. The process according to claim 1 wherein the coating is accomplished by an electrodeposition technique.

ymethyl) melamine.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5850.734" Dated November 26, 1974 Inventor(s) GIRISH GIRDHAR PAREKH et a1.

It is certified that error appears in the above-identified oatent and that said'Letters Patent are hereby corrected as shown below:

Column 4 line 25. After R insert are Column 6 line 40. After "solution" delete 250- Column 7 line 57. After "230 insert'-- Signed and sealed this 4th day of February 1975.

(SEAL) Attest:

McCOY M. GIBSON JR. C MARSHALL DANN Arresting Officer Commissioner of Patents FORM po'wso ($59) uscoMM-oc scan-Poo U.5. GOVIINIINT PRINTING oirlcl 2 1. O$.lll 

1. IN A PROCESS FOR HARD-COATING A METAL SUBSTRATE, THE IMPROVEMENT WHICH COMPRISES: COATING SAID METAL SUBSTRATE WITH A WATER DISPERSED COMPOSITION COMPRISING (A) FROM ABOUT 40% TO ABOUT 95%, BY WEIGHT OF AN ANIONIC ACRYLIC POLYMER, SAID POLYMER CONTAINING FROM 2.5% TO 50% BY WEIGHT OF MONOMER UNITS PROVIDING GROUPS OR FROM 0.5% TO 10% BY WEIGHT OF MONOMER UNITS PROVIDING ALCOHOLIC HYDROXYL GROUPS OR MIXTURES OF THE SAME, (B) FROM ABOUT 4.9% TO ABOUT 50% BY WEIGHT, OF AN AMINO ADEHYLDE CROSS-LINKING AGENT, SAID AGENT BEING UNETHERIFIED, PARTIALLY OR COMPLETELY ETHERIFIED, AND (C) FROM ABOUT 0.1% TO ABOUT 10% BY WEIGHT OF A TRIS SULFONYL METHANE HAVING THE STRUCTURE:
 2. The process according to claim 1 wherein the coating is accomplished by a dipping technique.
 3. The process according to claim 1 wherein the coating is accomplished by an electrodeposition technique.
 4. The process according to claim 3 wherein the heat treatment temperature ranges from 210*F. to 260*F.
 5. The process according to claim 1 wherein the metal substrate is zinc phosphated cold-rolled steel.
 6. The process according to claim 1 wherein the tris (sulfonyl) methane is tris (hexylsulfonyl) methane.
 7. The process according to claim 1 wherein the tris (sulfonyl) methane is tris (phenylsulfonyl) methane.
 8. The process according to claim 1 wherein the carboxyl group is derived from acrylic acid.
 9. The process according to claim 1 wherein the cross-linking agent is tetra (ethoxymethyl)-di (methoxymethyl) melamine. 